The present invention is generally directed to plastic headed fasteners and more particularly to an improved plastic headed fastener which exhibits higher applied torque before slip characteristics and which may be readily manufactured. The instant invention is further directed to an apparatus and method for manufacturing such an improved plastic headed fastener. An example of a fastener with a plastic cap having a depending skirt for controlling chips is disclosed and claimed in application Ser. No. 81,496, filed on Oct. 12, 1979, which is assigned to the assignee of this invention.
Metallic fasteners having plastic or other non-metallic covers overlying their head portions have found considerable utility. When driven into a work piece, such non-metallic head coverings can form a moisture barrier to prevent rusting or corrosion of the metallic heads.
Such fasteners as currently known in the prior art include a metallic body having a head portion and a shank portion extending therefrom. The shank is usually threaded and the head has an outer substantially circular perimeter. The plastic cover overlies the head and also defines a generally circular outer perimeter. Also, within the upper surface of the metallic head there is formed a oversized drive recess which is effectively reduced in dimension to a final size by the plastic cover.
Unfortunately, because the metallic head defines a circular perimeter, there is only slight interference fit between the head and cover. The cover therefore has a tendency to slip on the head upon the application of even modest driving torque to the drive recess. Obviously, such fasteners are difficult to use where high applied torques are required.
Furthermore, because the final drive recess must be accurately formed in the initial oversized drive recess of the metallic head, the initial oversized recess must be accurately aligned with respect to a complimentary mold projection used in forming the final drive recess. Since the outer perimeter of the metallic head is circular, this accurate alignment is difficult and time consuming to achieve during the manufacture of such fasteners.
It is therefore a general object of the present invention to provide a new and improved fastener of the type having a head portion covered by an overlying layer of non-metallic material.
It is a further object of the present invention to provide such a fastener which includes a head portion configured to prevent slippage of its overlying cover upon the application of applied torque to its drive recess.
It is a further object of the present invention to provide such a fastener which may be more readily manufactured.
More specifically, it is an object of the present invention to provide a metallic fastener blank having a head which includes an outer perimeter having at least one substantially straight side portion to provide increased interference fit between the head and head cover and which may also be utilized for readily aligning the over sized drive recess with a complimentary mold projection which forms the final drive recess within the head cover.
It is also a further object of the present invention to provide an improved apparatus and method for manufacturing such a plastic headed fastener.